When i texture paint in 2.8 how do i add shadows to see what im painting
When in Texture Paint mode and Rendered View go to Overlays on the top right.

At the bottom of the drop-down window for Overlays there will be a section Texture Paint and below it will say Opacity. If this is set to zero you will have full shadows on your model.

I find this makes it easier to paint directly onto the model and see where your paint is going.